Background: Acute lung injury (ALI) is the most serious pulmonary complication after lung resection. Although the beneficial effects of low-dose corticosteroids have been demonstrated in patients with postoperative ALI, there are limited data on optimal corticosteroid treatment. Methods: We retrospectively analyzed 58 patients who were diagnosed with ALI among 7593 patients who underwent lung cancer surgery between January 2009 and December 2016. Results: Of the 58 patients, 42 (72%) received corticosteroid treatment within 72 h (early treatment group) and 16 (28%) received corticosteroid treatment more than 72 h after ALI occurred (late treatment group). The early treatment group demonstrated a higher response to corticosteroid treatment compared with the late treatment group (95% versus 69%, respectively, p = 0.014), had an improved lung injury score (86% versus 63%, p = 0.072), and were more likely to be successfully weaned from the ventilator within 7 days (57% versus 39%, p = 0.332). During corticosteroid treatment, the early treatment group had a lower rate of delirium (24% versus 63%, p = 0.012) compared with the late treatment group. No significant differences in length of stay (30 versus 37 days, p = 0.254) or in-hospital mortality (43% versus 38%, p = 0.773) were observed; however, the early treatment group tended to have a higher rate of successful weaning than the late treatment group ( p = 0.098, log-rank test). Conclusions: Early initiation of corticosteroid treatment improved lung injury and promoted ventilator weaning in patients with ALI following lung resection for lung cancer.